Microphones

These are the primary tools for picking up sounds from vocalists, instruments and groups.

Knowing how they work, how to use them. and how to mix them

are key skills for an audio technician or engineer.

  • Transducer Type
  • Directivity
  • Characteristics
  • Applications
  • More Information
Transducer Type

Microphones are classified by the mechanism used to pick up sound pressure waves. The primary types are these:

Dynamic

In this type (moving coil), the sound waves strike a diaphragm that produces an electrical signal using a coil that moves in a magnetic field. This produces a signal in the microvolt range that is sent to an external preamplifier. This is the most commonly used type, and years of development have resulted in very robust designs with excellent frequency response. However, due to the nature of this structure, all tend to have some type of high-frequency resonance that shows up in the response curve.

Condenser

In this type, the movement of a thin, electrically charged diaphragm, creates a small varying voltage that is then amplified internally and sent to an external preamplifier. A common type, an Electret, has a permanently polarized capacitor element. Both types require phantom power to drive the electronics inside the microphone needed to amplify the signal from the condenser element. For this reason, condenser mics tend to have a higher self noise than dynamic mics and are somewhat more fragile. These mics tend to have great sensitivity with a wide and smooth frequency response.

Go here for an excellent video on dynamic and condenser mics as transducers. MXL also has a good page on condenser mics,

Ribbon

In this type of dynamic microphone, a thin metal ribbon moves in a magnetic field to produce the electrical signal. This design results in a diaphragm that is very light and thus more responsive than the moving coil design, but it also produces less output, requiring a transformer to step up the voltage. This design generally has less output than a moving-coil dynamic mic, and it also has a natural figure-eight directionality. A ribbon mic has a very uniform frequency response across the front of the mic and a nearly identical response across the back. As the sound level decreases when you get off-axis, it still sounds like the original source. And the sound pickup from the sides of the mic (90 degrees off-axis) is completely nonexistent. You can’t use them everywhere, but where you can, they give good results. Sweetwater has an excellent article on Ribbon Mics.

Guitar Pickups

A standard microphone can be used for recording the sound from a guitar and for live sound in many situations. An electric guitar, whether a true electric or an acoustic guitar fitted with a pickup, requires a device to convert the string motions into an electronic signal. The pickup device is not a microphone, as discussed here, but is mentioned for completeness. See the Ehome Recording Studio and the Guitar World sites for more details. Sweetwater also has a good page – How do Pickups Work?

While there are other types of microphones, they are seldom used for audio performance purposes. Select the More Information tab to learn about other types of microphones.

Directivity

Microphones are also classified by the directional nature of their pickup pattern. There are 4 basic types:

Omnidirectional – This type picks up sounds from all directions.

Cardioid – This type picks up sound in one direction primarily – the front – and less sound from the rear.

Hyper-Cardioid – This is a slightly more directional version of a cardioid microphone.

Bi-directional – This type picks up sound primarily from the front and rear and significantly less from the sides.

The above diagram show four different idealized polar patterns..

Since they are symmetrical about the vertical axis, the angles are measured

left and right from zero to 180 degrees

Click here for a more detailed explanation of these diagrams.

A number of microphones, both handheld and studio types, can be switched among several directivity patters, providing more options for their use in different situations. Examples include the Shure KSM9 series, the AKG C414, The SE T2, and the Blue Yeti Pro.

IsaacsMusic has an excellent article on mic polar patterns with a video/audio demonstration of the C414.

Characteristics

Every microphone is manufactured to have a combination of features that match the goals set by the designer. Certain characteristics are a natural consequence of the transducer type, while others are meant to enhance the microphone’s ability to perform in various situations. For example, a vocal mic used on stage needs to be fairly rugged, while one designed for studio recording can be less so. This causes dynamic mics to be used more frequently on stage applications than condensers, since the latter have a transducer and electronics inside that require a power source and may not take rough handling as well as the former. Ribbon mics are even more fragile, and they have a somewhat limited high-frequency response, so their applications are fairly specialized.


One thing that is important to hand-held microphones is handling and cable noise. A well-designed mic such as the Shure SM58 has a very effective shock mount that protects the capsule and virtually eliminates handling noise. This property is one that separates well-made mics from cheap knock-offs.

A vocal mic can have a more limited and perhaps “sculpted” frequency response curve, while one designed for picking up instruments and acoustical testing needs to have a smoother and wider frequency response. In fact, such mics are usually called “instrumental” mics and are usually condensers. An omni-directional mic is a pure pressure-sensitive transducer and tends to have a flatter response than a directional mic. The design of a directional microphone tends to result in what is called the “proximity effect.” This phenomenon causes the low frequencies below about 200 Hz to be increased relative to the higher frequencies. This is because sound from the around the mic is directed to the back of the transducer in a manner that reduces the response from the rear – a pressure-gradient transducer. See below for more information on the proximity effect. As the source gets within a few inches of the directional mic, there is not only an increase in volume, but also an increase in bass response. The diagram to the right show the response cu